Selenium is a trace mineral found in foods and soil. How much you get from the foods you eat varies depending on where the food was grown. Some soils are deplete of this mineral. Selenium can be taken in the diet through organ meats, shellfish, fish, nuts (Brazil nuts in particular) and grains. Selenium became of interest to researchers in the eighties since not much was known about its role in metabolism. Since then, it is now known that selenium is vital to thyroid function and immune responses. Moreover, it is essential in proper growth, development, reproductive function and overall metabolism. It is also a powerful antioxidant.
SELENIUM AND THYROID FUNCTION
When selenium is taken in from the diet it is used to synthesize seleno-enzymes (proteins). There are 3 classes of selenoproteins that the body makes which include gluthathione peroxidases (GPx), thioredoxin reductases (TRx) and iodothyronine deiodinases (DIs). GPx is a powerful antioxidant that cells use to prevent oxidative stress particularly important to cell membranes. TRx is involved with cell structure and growth and DIs are involved with converting thyroid hormone T4 into T3, the active form. The highest concentrations of selenium are found in the liver, kidneys and thyroid. Selenium also aids in normalizing testosterone and estrogen levels. It aids in removal of lipids and phospholipids reducing cholesterol levels. Low levels of selenium are associated with depression and mood disorders. Suggested dosage runs between 200-400mcg daily.
The selenoprotein group DI are enzymes that convert the storage thyroid hormone T4 (thyroxine) into the active form known as T3 (triiodothyronine). These selenoproteins do so by removing an iodine from T4. During the process of making T4 in the thyroid, hydrogen peroxide is produced and is a toxic by-product. Selenium comes to the rescue in the form of Gpx (glutathione enzyme). GPx neutralizes hydrogen peroxide thus preventing oxidative stress while TRx uses NADPH (nicotinamide adenine dinucleotide phosphate) to re-reduce thioredoxin in the formation of deoxyribonucleotides. This prevents thyroid cell damage and death.
Selenium ACE is a combination of the mineral selenium along with vitamins A, C and E. Vitamin C is another water soluble antioxidant which has the ability to regenerate Vitamin E. Vitamin E is fat soluble and as such has the ability to protect cell membranes internally. Vitamin A is important for the health of eyes and skin and is useful for gastrointestinal disorders. It is also important for bone and teeth formation, fat storage and protects you from colds, flu and other respiratory ailments. It acts as an anti-aging agent and helps the body utilize protein. Vitamin A is available as fish liver oil and Beta Carotene (a pro-vitamin A). The body has the ability to make vitamin A from the pro form. Vitamin A is important to the immune system and supports selenium function. Selenium and vitamins A, C and E work synergistically to support proper cell function.
SELENIUM AND IMMUNE FUNCTION
Selenium is an essential component of the selenocysteine-containing protein which is important for many aspects of cell biochemistry. This suggests that selenium is also important for immune function and in particular neutrophil function. Neutrophils are a type of white blood cell involved with destroying certain foreign organisms. During the process of destroying these foreign organisms, many free radicals are produced from the breakdown of these pathogens in the form of hydrogen peroxide. That’s where glutathione peroxidase comes in with its ability to chemically break down this toxic molecule. Recall that selenium is required to make glutathione and a selenium deficiency will impair immune function bringing about a whole host of diseases. Research has brought to light that a selenium deficiency often occurs when there is a vitamin E deficiency as well. This mineral and vitamin act as an oxidant/antioxidant couple and both are required for proper function. The biochemistry of selenium is a complex system involving the expression of a wide range of proteins that use selenium many of which remain to be elucidated.
At least 5 gluthathione peroxidases have been characterized to date where some act in the extracellular space, cytoplasm of the cell and in association with cell membranes. Moreover, selenium is important to the gastrointestinal tract maintaining a healthy immune system there protecting the gut from colitis and other inflammatory responses by acting as a powerful antioxidant.
So far, 25 genes have been isolated that code for selenoproteins in the human genome providing for some 30 or more different proteins through alternative splicing. What this means is that selenium has essential functions in redox control of many metabolic functions across many cells far beyond thyroid hormone metabolism. Selenium function is known to extend into transcription factors involved with turning genes on and off. Research indicates that selenium has a tremendous influence on the immune system in many ways depending on the current state of the body/brain.
Researchers report that selenium has the ability to influence both the innate and acquired immune systems. The innate system involves barriers to infection such as skin along with macrophages. Macrophages are white blood cells that have the ability to engulf foreign materials and pathogens, take them inside themselves and degrade them effectively cleaning up an infected area. Selenium also affects antibody production. Animal research has demonstrated that rats deficient in selenium decreases their IgM, IgG and IgA titers (antibodies) and in humans IgG and IgM titers are decreased as well.
The acquired immune system encompasses T and B cells as the major effector cells that mature over time with exposure to foreign invaders and are specific for that invader. Macrophages not only breakdown pathogens, they also have the ability to become antigen presenting cells (APC). Once they break down a pathogen, they can activate T cells in an acquired immune response. When B and T cells are activated they clone themselves. Some of the clones become active and others become memory cells. When B and T cells are deficient in selenium they have difficulty in making copies of themselves. This effectively decreases the immune response. In the case of selenium deficient macrophages, the macrophage has difficulty in making Leukotriene B4 which is needed to signal neutrophil chemotaxis. Neutrophils require this signal to migrate to the site of injury.
Once a neutrophil has taken in a pathogen, the pathogen is taken into a phagolysosome where enzymes will break it down. This membrane-bound compartment inside the neutrophil contains superoxide-derived radicals that are used to kill pathogens. This is a delicate balance between producing enough radicals to kill the pathogen and yet not kill the neutrophil. If the neutrophil enzyme systems that are used to degrade these radicals are working properly there is no problem. Research demonstrates that animals with neutrophils deficient in selenium have no problem ingesting foreign materials but are less capable of killing the pathogen. This is linked to decreased cytosolic glutathione peroxidase activity which in turn causes the superoxide-derived radicals to kill the neutrophil. In other words, the neutrophil is digesting itself. This immune system malfunction due to selenium deficiency is also compounded with a concomitant hypothyroidism also due to selenium deficiency. Hypothyroidism adversely affects immune function by impairing the neutrophil to respond to a foreign entity.
It is reported that individuals in the UK who consume diets that are below the British Recommended Daily Intake should supplement with selenium to maintain proper immune system function. Selenium deficiency may increase the risk of general immune system weakness, increased cancer incidence and increased susceptibility to virus and flu. A study was done on 22 healthy UK patients to determine if selenium supplementation would provide changes in the rates of clearance and mutation of a live attenuated polio vaccine. All patients had low plasma levels of selenium. Sixty percent received 50 or 100 mcg of sodium selenite and the rest received placebo daily for 15 weeks in a double-blind study. All patients received the oral live attenuated poliomyelitis vaccine after 6 weeks and enriched stable (74)Se intravenously 2 weeks later.
These researchers report that selenium supplementation increased plasma levels of selenium, the body exchangeable selenium pool and lymphocyte phospholipid and cytosolic glutathione peroxidase activities. Cellular immune response increased by way of increased production of interferon gamma as well as other cytokines with an early increase in T cytotoxic cell proliferation as well as T helper cells. No change in humoral function was reported (antibody production). These researchers also report that patients who were supplemented with selenium cleared poliovirus faster than those taking placebo. Furthermore, poliovirus reverse transcriptase-polymerase chain reaction products taken from feces of the selenium supplemented patients contained a lower number of mutations. The take home message is that patients who had been supplemented with selenium were were able to handle a poliovirus load. Whereas those that received placebo were not. This study suggests that taking 100 mcg of selenium may be sufficient to support optimal immune function.
Decreases in dietary intake of selenium due to poor soil conditions have led sub-optimal thyroid and immune function. Supplementation with Selenium ACE may aid in restoring a selenium deficiency thereby boosting thyroid and immune function.
The role of selenium in thyroid hormone metabolism.
Selenium Critical to General Health and Thyroid Function
How Can Selenium Help the Thyroid?
Selenium in the Immune System
An increase in selenium intake improves immune function and poliovirus handling in adults with marginal selenium status.
Selenium Promotes T-Cell Response to TCR-Stimulation and ConA, but Not PHA in Primary Porcine Splenocytes